One component of forage harvesters is a forage cutting unit which receives crop material, such as haylage, oat silage, mature corn silage, or ear corn silage, cuts it into small pieces and discharges the pieces rearwardly, usually into a trailing wagon. In the past, forage cutting units have had two major functions; (1) to cut crop material and (2) to propel the material rearwardly with sufficient velocity to carry the material to the trailing wagon.
The cutting units generally comprise a horizontally disposed housing having a front inlet and rearwardly directed discharge outlet. A stationary shear bar is mounted at the lower edge of the inlet. A cylindrical cutter having cutting knives mounted on a cutterhead is rotatable within the housing. The knives move downwardly past the shear bar and then rearwardly toward the discharge outlet.
In the past, the propulsion of the material through the discharge outlet has come partly from the centrifugal throwing action of the knives and partly from the air current generated by the fast moving knives and cutterhead. In recent years, the function of the cutter in propelling the cut material rearwardly has been largely replaced by use of an independent blower to propel the cut material. Forage harvesters employing an independent blower have the advantage that a stationary recutter screen that coacts with the rotating knives of the cylindrical cutter can be placed at the discharge side of the cutting unit to provide substantially uniform, complete and fine cutting of the crop material.
A recutter screen is a curved, semi-circular, plate that conforms to the cylindrical cutter and contains many holes or perforations over its entire surface. The recutter screen is made to fit under the rotary knives of the cylindrical cutter and is normally set in a position where the rotary knives almost touch the inside surface of the screen. The inside surface of a recutter screen preferably presents a large number of cutting surfaces that coact with the rotary knives. The recutter screen causes the forage to be held in the cylindrical cutter and to be re-cut by the rotary knives until the forage can escape to the discharge outlet through the holes of the screen.
To achieve substantially uniform length cutting of forage, the stems of the forage should be on a line parallel to the direction of travel through the cutting mechanism. Swathers, windrowers, or mowers and crimpers which prepare the forage for feeding to a forage harvester, however, usually do not align the forage parallel to the direction of travel and present a serious problem to the forage harvester in maintaining a uniform length of cut. Most forage harvesters will pick up a windrow in the same manner in which it is laid down and thus do not materially change the position of the stems in the windrow. The harvester picks the stems up and conveys them through the feed rolls and cutting mechanism without altering their position. The harvester may move the forage sidewise for a short distance, but it will not materially change the relation of the stems to the direction of travel. Thus, material which is laid parallel in the windrow, will remain parallel and stems which are crosswise will pass through the feed rolls and cutting mechanism crosswise. The function of the recutter screen is to deflect the long stems as they leave the cutterhead to enable the rotary knives to cut them one or several times more to bring them to a substantially uniform length.
A recutter screen actually serves several different purposes depending upon the type of material which is being recut. For example, in cutting haylage the recutter screen is used to reduce long stems, that pass through the cylindrical cutter perpendicular to the direction of travel, to a uniform short length, but not to shorten the actual length of the cut of the bulk of the material.
When grinding ear corn, the recutter screen is used to retain the particles of ear corn within the cutting cylinder until the larger particles are reduced to a fine enough consistency so that they will pass through the small diameter holes in the recutter screen. In cutting a sudan-sorghum mixture a recutter screen is used to break up any long stems which may have passed through the feeding mechanism at an angle to the direction of travel. Also, recutter screens are used in harvesting whole corn silage to prevent long pieces of leaves, stalks or "nubbins" of ears from passing through without being cut to a uniform length.
The use of a recutter screen has numerous advantages, For example, the use of a recutter screen increases the palatability of resulting feed because the reduction of all material to uniform length avoids the problem of cattle sorting out long stems, pieces of ears, and material which if not reduced to a uniform length, becomes objectionable to their taste. Tests indicate cattle fed recut material will leave no portion of the stalk or ear in the manger since all of the corn plant including stalk and ear, have been reduced to a uniform consistency whereas cattle will leave the long stems, pieces of stalk and parts of ear of material cut without a recutter. The cutting of haylage to a uniform length by a recutter screen results in denser pack of the material and enables from 20% to 40% more material to be stored in a silo or structure. Further, the denser pack of silage eliminates more air and reduces spoilage. Recutting material in the field eliminates the need for special recutting equipment at the silo or structure. The more uniform cut achieved with a recutter screen also permits a denser pack in the wagon and results in fewer trips between the field and the storage area.
Until the present invention, the prior art has taught that multiple cutting-surface recutter screens were necessary to achieve the desired fine and uniform cutting of random oriented forage as picked up from a swath or windrow. Although the use of a recutter screen provides numerous advantages, forage harvesters having recutter screens require significantly more power to operate the cutting mechanism. Further, recutter screens have a tendency to overcut the forage material being fed to the cutting mechanism because the forage material is usually carried around the periphery of the cutter housing a number of times before it passes through the holes of the recutter screen even though it has reached a size where it can pass through the holes.